Cortical hypometabolism demonstrated by PET in relapsing NMDA receptor encephalitis

N-methyl-d-aspartate (NMDA) receptor encephalitis is a newly defined type of autoimmune encephalitis. Two girls (age 3 years, case 1, and 7 years, case 2) with relapsing NMDA receptor encephalitis each had the classic clinical features of encephalopathy, movement disorders, psychiatric symptoms, seizures, insomnia, and mild autonomic dysfunction. Both patients had persistent neuropsychiatric disability, despite immune therapies. Positron emission tomography (PET) scans were performed during clinical relapse at 6 weeks (case 1) and 5 months (case 2). In both cases, the scans demonstrated reduced fluorodeoxyglucose metabolism in the cerebral cortex, with the temporal regions being most affected. PET imaging was more sensitive than magnetic resonance imaging in these patients. In contrast, the one previous report of acute NMDA receptor encephalitis indicated cortical hypermetabolism. Thus, NMDA receptor encephalitis may be associated with variable PET findings, possibly dependent upon the timing of the study, or other factors. Future studies should investigate whether cortical hypometabolism is associated with a relapsing course, and whether it is predictive of a poorer outcome in NMDA receptor encephalitis.